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Winroddier Vs interferogram comparison?

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#1 William Mc

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Posted 24 November 2013 - 01:42 PM

With all the talk lately of SCT quality, I'm now interested in the true optical quality of all my scopes. I read a lot about subjective, off the cuff assessments, and time, and location distanced comparisons. I'm more in tune with the scientific method, and would prefer hard numbers. Also, it would be handy to have a benchmark database as to make comparisons against. The gold standard appears to be Sterhl ratings generated by interferogram testing. A secondary advantage to this type of assessment is the readily accessible, ready made database provided by Rohr's interferogram tests. The main negative seems to be that interferogram testing must be done in a Lab using expensive equipment, and is out of reach of average users / owners. Therefore, the scopes must be shipped for testing, and this entails a considerable cost, as well as a risk, especially with larger scopes.

As an alternative to Physical testing, the "Free" Winroddier software is able to generate the same testing data-points using a simple webcam. This would appear to be the answer, but how well can these numbers be trusted? If the test is carefully done with a cooled scope, if decent seeing, and using a high speed Mono cam, just how close can this test come to true interferogram lab tests?

Has anyone actually made a real comparison, of the numbers generated by Winroddier, and a physical lab test? How close can it come?

.02 Sterhl? .05 Strehl?

Is Winroddier accurate to make direct comparisons against interferogram lab test results, and avoid the considerable risk of shipping damage?


I'd like to hear from everyone, but especially those on the forum very familiar with Winroddier testing. Freestar? Desert rat?

I have done Winroddier tests before under less than good conditions, and with a lower quality cam, but now that I have a observatory, and a higher quality, high speed mono cam, I want to make a better go of it. I'd like to come up with the most accurate, repeatable, standaridzed process to assess all my scopes, and future ones. Perhaps this process should include an artificial star?

I'd love to see discussion as to how this test can be made more accurate as to make comparison against Rohrs extensive database.

Update: I just discovered that the English version of the latest Winroddier 3.0 has been released. Fantastic news!

#2 Jared

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Posted 24 November 2013 - 03:35 PM

I haven't compared Winroddier to an interferogram, but I will say that getting consistent results out of Winroddier is not exactly a trivial matter. You need to get your technique down--primarily the correct amount of defocus, perfect or near perfect collimation, and the exact same amount shift on either side of focus. When I was first trying out Winroddier I got results on my scope that varied from 0.60 Strehl to 0.91 Strehl. Unless you know what you are doing it is hard to trust the reports.

With some practice, though, I have been able to get much more consistent results on my scope--repeatable within 0.05 Strehl or so. Are they correct? I have no way to validating. I would certainly recommend taking results you see on forums with a grain of salt.

#3 DesertRat

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Posted 24 November 2013 - 04:17 PM

You have posed a timely question!

Wade is in the process of writing an updated cookbook for WinRoddier (WR). It is hoped it will help users overcome the pitfalls and common mistakes made in its use.

WR does a brilliant job, assuming the user obeys a fair number of rules.

Its tough to beat an IF test. However speaking for myself I would never ship a scope in order to satisfy any curiosity. I might take it across town if that service was available. Any test has its limitations and like statistics or computer benchmarks, needs to be performed and interpreted carefully.

Some of Rohr's tests were performed on scopes with alignment, collimation and thermal issues. Note to the CN'ers who like to assume more than was intended in my comment - I respect what Rohr does. But a test that one can perform themselves, and with practice quickly, all the while making possible adjustments, has great utility for a backyard astronomer.

Accuracy better than 5% is likely if the test is done properly 2% and better is possible. The number of caveats I would have to add in this statement is too lengthy to detail here, but includes things like seeing limitations, noise, gamma, stacking video processes, avoiding any processing of the images except cropping, image masking within WR, etc.

One troublesome issue with WR is the flavor of FITS files that it requires. Some of that constraint has been relaxed hopefully with a utility I wrote called WRFITS, which formats FITS or Tiff files for reliable WR input. This allows users to take the extra focal frames, stacked in AutoStakkert for example, run it thru and then into WR.

If you want to validate WR take a look at test files I created in the yahoo Roddier Test group files folder called "WinRoddier simulation tests". In there are some notes of interest. The files show 20nm rms of various aberrations at 20 waves defocus for a 130mm f9 refractor.

Hope this helps. More later!

Glenn

#4 Wade Van Arsdale

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Posted 24 November 2013 - 05:44 PM

Wmacky,
We're very close now on an updated WinRoddier User Manual Specific for Ver. 3 WR. It will hopefully address and give solutions for most of the pitfalls that decrease accuracy in the test (and there are quite a few!).

I have two instruments (one refractor and one corrected Dall-Kirkham) that I have known bench lab tests on that WR did very well on, with a spread of about 0.02 Strehl across multiple test datasets with variable atmospheric turbulence from night to night while testing was going on. Some tests nailed it dead-on as well.

I don't think you'll ever beat a well-done bench interferometry test with WR, but it will sure get you very close *if* all the environmental variables are well-controlled in the setup. The new manual will get into all that in pretty good detail. I hope to have it released to the Yahoo Roddier Group this week, along with a bunch of auxillary user guides for the support apps involved as well.

My goal was to try to find a path through all the difficulties of doing this test and make it more streamlined for lay people like myself who didn't have optical/engineering/math backgrounds.

Note, this is a complete rewrite with all new support apps built to run on 64-bit Windows pc's, thanks to some very fine app-writing by our own Glenn Jolly ("Desert Rat" from here on CN). The new steps will be much more streamlined than the older methods, with hopefully less that can go wrong on the software side of things.

So stay tuned....it's coming very soon!

Thanks,
Wade Van Arsdale
Little Rock, AR., USA.

#5 William Mc

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Posted 24 November 2013 - 05:56 PM

Glen, This is all overwhelmingly good news.

I have questions!

1.Great news about the new cookbook. Any word when it will be complete?

2.I had not heard of your utility, but had been hoping for one like it for a long time.Thank you! Thank You! ( Has this been announced elsewhere?) Is it finished? Where can I get it! Could this utility and new cookbook be what was needed to get everyone using WR instead of all these subjective declarations?

Perhaps with everyone generating data, we can finally get a handle on quality range expectations of these mass produced scopes instead of guesses, and small sample extrapolations!

3 Wades last post in the last WR thread in this forum stated that he now believed more defocus was needed for more accurate strehl results. This seems to be in contradiction to the need he found for small Fits files "120pixels" I never heard anything else? Was he able to resolve this question? Binning?

#6 William Mc

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Posted 24 November 2013 - 05:58 PM

Wmacky,
We're very close now on an updated WinRoddier User Manual Specific for Ver. 3 WR. It will hopefully address and give solutions for most of the pitfalls that decrease accuracy in the test (and there are quite a few!).

I have two instruments (one refractor and one corrected Dall-Kirkham) that I have known bench lab tests on that WR did very well on, with a spread of about 0.02 Strehl across multiple test datasets with variable atmospheric turbulence from night to night while testing was going on. Some tests nailed it dead-on as well.

I don't think you'll ever beat a well-done bench interferometry test with WR, but it will sure get you very close *if* all the environmental variables are well-controlled in the setup. The new manual will get into all that in pretty good detail. I hope to have it released to the Yahoo Roddier Group this week, along with a bunch of auxillary user guides for the support apps involved as well.

My goal was to try to find a path through all the difficulties of doing this test and make it more streamlined for lay people like myself who didn't have optical/engineering/math backgrounds.

Note, this is a complete rewrite with all new support apps built to run on 64-bit Windows pc's, thanks to some very fine app-writing by our own Glenn Jolly ("Desert Rat" from here on CN). The new steps will be much more streamlined than the older methods, with hopefully less that can go wrong on the software side of things.

So stay tuned....it's coming very soon!

Thanks,
Wade Van Arsdale
Little Rock, AR., USA.


WOW!!!!!!!!!!!!!!!
This all just fantastic! You are a service to this community. I so glad I posted this thread!~

#7 Wade Van Arsdale

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Posted 24 November 2013 - 06:06 PM

Wmacky,
Yes, we believe the "how much defocus" issue for most consistent WR3 results is now solved. I go into that in quite a bit of detail in the new manual, with an Appendix at the end to work through the math and some examples using 15 waves. Here is what my datasets (many dozens of them) have indicated (note, it's a two-fold thing on-screen size vs. waves of defocus):
1) 15-20 waves defocus is the *minimum* amount of defocus for best practices with WR3.
2) In my datasets, I got the most consistency with on-screen star diameters of 100-150 pixels with 100-120 being my absolute best and most consistent repeats in most cases.
3) On-screen size to allow you to hit this 100-150 pixel target can be gotten by a couple of other ways besides just amount of defocus:
a) Camera Binning
b) Camera's pixel size (not overall chip size, but the micron size of its individual pixels).

In the manual, I work through a couple of scenarios where your on-screen star diameter might not fall in the target zone, but you can fix this by using a combination of (or both) of the tweaks above.

Also, "ROI" is addressed in some other scenarios that help the processing be more accurate.

I hope to have it out sometime this week or possibly next weekend after Thanksgiving.

(P.S...agree, what we need is a LOT of data from other end-users....this is a work in progress, so the more data from multiple users we get, the better!!).

Thx,
Wade

#8 William Mc

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Posted 24 November 2013 - 06:17 PM

Wmacky,
Yes, we believe the "how much defocus" issue for most consistent WR3 results is now solved. I go into that in quite a bit of detail in the new manual, with an Appendix at the end to work through the math and some examples using 15 waves. Here is what my datasets (many dozens of them) have indicated (note, it's a two-fold thing on-screen size vs. waves of defocus):
1) 15-20 waves defocus is the *minimum* amount of defocus for best practices with WR3.
2) In my datasets, I got the most consistency with on-screen star diameters of 100-150 pixels with 100-120 being my absolute best and most consistent repeats in most cases.
3) On-screen size to allow you to hit this 100-150 pixel target can be gotten by a couple of other ways besides just amount of defocus:
a) Camera Binning
b) Camera's pixel size (not overall chip size, but the micron size of its individual pixels).

In the manual, I work through a couple of scenarios where your on-screen star diameter might not fall in the target zone, but you can fix this by using a combination of (or both) of the tweaks above.

Also, "ROI" is addressed in some other scenarios that help the processing be more accurate.

I hope to have it out sometime this week or possibly next weekend after Thanksgiving.

(P.S...agree, what we need is a LOT of data from other end-users....this is a work in progress, so the more data from multiple users we get, the better!!).

Thx,
Wade


Fantastic!

I had plan to start testing over the holidays, and this is unbelievable. Please give me a heads up when it's all posted.

#9 DesertRat

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Posted 24 November 2013 - 06:30 PM

Wmacky,

By now you know that I'm not writing the manual. I've helped some. As far as when - Wade is waiting on me right now. :crazy:

The WRFITS utility is located and described at the yahoo group noted earlier.

I recommend defocus of at least 15 waves, but believe it better to use 20-30 waves. For scopes of long efl that requires binning assuming pixels in the 4-6um range. Too little defocus leads to poor numerical solutions, optimistic and otherwise. Visual star testers will recognize the difference here. Small defocus magnifies aberrations greatly, but Roddier analysis is based on subtle illumination gradients across the pupil and any non-circularity.

The extra focal images should cover approx 80-132 pixels. That represents thousands of sample points. You can have larger images but there is a price to pay for the increased noise from the gain required.

Finally, it should be pointed that out an IF report is not like some kind of gold standard NIST piece of paper. I have several certficates I received, commented 'thats nice', and filed away never to be seen again. All that really matters is how a scope performs for you. IF tests have there own set of caveats, and depending on the hardware and the tester a report can be of value or pure rubbish.

Thanks Wade for your posts, sorry if I blew your cover on this! :p

Glenn

#10 Wade Van Arsdale

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Posted 24 November 2013 - 11:05 PM

No prob. Glenn. And I would add that without Glenn's app-writing and help in explaining the optical theory and math to me, this project never even gets off the ground. So the thanks go to Glenn on this. I think you guys will be pleased with the results. We'll post back here as soon as we're done and it's out there.

Thx,
Wade

#11 saemark30

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Posted 26 November 2013 - 06:06 PM

Seems one needs to use a monochrome camera which can save in FITS.
Or can one use a DSLR and convert those images into the proper format?

#12 DesertRat

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Posted 26 November 2013 - 08:03 PM

You can extract the green layer from a raw DSLR frame. The software for most DSLR cameras have a mechanism to create a 16 bit Tiff image. If possible avoid the 8 bit Tiff format. Using WRFITS you can convert to the FITS format WinRoddier requires.

You can find WRFITS at the yahoo "Roddier Test" group files area:
Files Utilities for WinRoddier\
WRFITS.zip FITS & TIFF Image conversion utility

You may use an image processing program to convert the RAW frame to 16 bit FITS format. Its important NOT to do any processing other than cropping. No contrast stretching, sharpening, etc. The FITS image must conform to pixel values of from 0 to 64000. If it does not then one can also use WRFITS for that.

A new cookbook manual will be released soon.

Glenn

#13 William Mc

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Posted 26 November 2013 - 09:08 PM

A new cookbook manual will be released soon.

Glenn


Checking twice a day! :grin: :jump:


BTW. I've downloaded the utility had it's great. Just what I was pleading for in the other large thread from August. Hats of to you for the effort. There will be no longer be an excuse for someone wanting to know!

#14 jhayes_tucson

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Posted 27 November 2013 - 12:33 AM

Seems like a Hartmann (or better Shack-Hartmann) test would do the trick with a lot less Vodoo.

#15 DesertRat

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Posted 27 November 2013 - 10:44 AM

John, not sure what 'VooDoo' elements you are referring to.

The image format requirements of WinRoddier have been problematical. If the developers had, for example, used the CFITSIO library we would have experienced fewer problems with the restrictions on image scaling. The WRFITS program I wrote uses standard libraries hopefully to make this a little easier. We will see if that really is the case, but the since the user base is fairly small it might take some time before we know.

The Roddier method does seem almost magical, and one might be tempted to feel its almost too good to be true - is that Voodoo? Like any testing method its only as good as its execution all the while understanding its pitfalls and limitations. Hopefully most of those will be made clear when the updated cookbook is released. Like any test method requiring better numbers, collections of data are needed to do proper statistics. I find that far more valuable than the accumulation of all the anecdotal information (if not just made up or rumors overhead at the local bar) seen on this forum!

WinRoddier makes use of the Mahajan annular zernike set. Since that is directly applicable to the scopes on this forum, I think it deserves some thought in evaluating its potential, rather than simply dismissing it as Voodoo.

The Shack Hartmann idea is interesting, but has some limitations particularly for smaller telescopes. The unavailability of good inexpensive micro lens arrays as well as the software required to do the analysis make it, at least for now, just an idea.

One example of where the Roddier technique was beneficial to me was identifying the backfocus characteristics of the EdgeHD telescope. I knew the theory of it, but having real numbers was quite valuable. Also with a monochrome camera and filters I could evaluate the dependence of spherical correction on wavelength. Again spherochromatism predictions are nice, but real numbers better.

Optical testing should consume a only a small fraction of an amateur astronomers time. Once the Roddier method is mastered, rapid evaluation is possible. Happily it need only be done one time, until that time a configuration change is made.

Glenn

#16 Wade Van Arsdale

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Posted 28 November 2013 - 12:55 AM

The new user manual for WinRoddier Version 3 is now available for upload at the Yahoo Roddier Test Group. It is located in the Files > "WinRoddier Ver. 3" folder of the group.

Also you can download it from this alternate site:
http://www.compubuil...User_Manual.pdf

This is a total rewrite of the WinRoddier file capture and file prep methodology using new support apps written by Glenn Jolly from here on the CN Forums and other apps.

We've tested the new methods extensively with many datasets used, and found them to work well with the latest iteration of WinRoddier software (Version 3).

There is extensive setup help included in the manual to get you through some of the common pitfalls encountered when doing the test and collecting WinRoddier data.

You can also download some sample files for use to help familiarize yourself with WinRoddier if you are new to it. You can get them from the Yahoo Roddier Group Files section, same folder as above, or you can download them from this alternate link:
http://www.compubuil...ample_Files.zip

The .zip file contains a Readme.pdf file with the telescope and camera setup parameters that you will need to plug in to WinRoddier to analyze the .fits files that are also included in the .zip file.

Good luck, and let Glenn ("DesertRat" handle here on CN) or me know if you find any errors in the user manual or other help manuals.

I encourage anyone wanting to try this to post any help queries over in the Yahoo Roddier Group where the bulk of the WinRoddier end-users hang out.

Thanks,
Wade Van Arsdale

#17 William Mc

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Posted 28 November 2013 - 02:12 AM

I'm going to dig into it tonight!

#18 Wade Van Arsdale

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Posted 01 December 2013 - 12:58 PM

Hello Group,
Glenn Jolly has come up with a neat utility to pre-calculate the on-screen star diameter you will need to use for a given amount of waves of defocus when shooting WinRoddier data. This is a huge time-saver and kills any chances for making math errors when pre-calculating manually.

You can download the new utility from the Yahoo Roddier Groups Files > WinRoddier Ver. 3 folder, or from this alternate link if not a group member:
http://www.compubuil...load/WRCALC.zip

(Readme file with instructions is included in the .zip file).

Also, I've updated the main WR Ver. 3 user manual to reflect this new app, with instructions for it included in the manual. Available from same Yahoo Roddier Group folder, or here:
http://www.compubuil...User_Manual.pdf

Please direct any inquiries on the new app or requests for help to the Yahoo Roddier Group.

Thanks to Glenn Jolly for his great work on the WinRoddier helper apps!!

Wade

#19 William Mc

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Posted 01 December 2013 - 01:29 PM

I just double checked my manual calcs I had already made against Glenn's new utility, and all were correct! I surprised I didn't screw it up. There used to be a lot of required calculations!

Guy's, and gal's,
I spent some time over the holidays checking out the new manual, and the new testing utilities. Let me tell you everything has completely changed. If your ever had attempted to Roddier test your scopes optics, you know what a long, and tedious process it used to be. Many were never even able to get a result. Well that has all changed. If you have any curiosity as to your scopes Strelh numbers, there is no reason not to find out. SAll you need is a planetary imaging cam, or even a web cam, and a free night of good seeing.

I would like to personally thank Wade, and Glenn
(Desert Rat) for taking their valuable time to provide this help to the community.

Well done guys! :jump:

Wade, Perhaps this info should be posted in the "General" forum so that more will see it?

#20 drago

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Posted 01 December 2013 - 02:12 PM

good seeing starry night is very valuable, because it not frequently thing at all.
maybe hubble optics artificial star for 20 bucks and a cloudy night is far better?
there is no need a computer at all?
linux version?

#21 Wade Van Arsdale

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Posted 01 December 2013 - 03:59 PM

Hello Drago,
The problems I've frequently run into with artificial stars are twofold:
1) Ground thermals ruining the data.
2) Not enough grounds-space to back away far enough from the light source for a small-enough point source for good analysis.

It's far easier for me to pick a good seeing night, setup my scope at home and point it straight up than try to find a remote location, then have to transport the whole rig out to the site to use the artificial star.

Now that's not to say these are universal problems for everyone, so it's worth a shot if you can overcome those kinds of logistical issues.

You will always need a computer and camera though if you are going to do WinRoddier data capture and software analysis.

Also, WinRoddier has a pretty good ability to overcome some level of seeing turbulence, especially with modern fast video cameras and large stack sizes. So the night doesn't have to be perfect to be able to capture good WinRoddier data....just "pretty good" seeing is good enough much of the time for good WR results....specifically 2.5 arc-sec FWHM seeing or better will usually work OK for WR using the video camera methods described in the new manual.

Re. Linux versions of WR, you will need to ask the AstroSurf developers about that or go to their website. Link can be found on Google Search.

All the helper apps Glenn has done for WR are for use in Windows XP/Vista/7 32 or 64-bit...no Linux version available as far as I know, and I don't know of any plans to do that.

Cheers,
Wade

#22 jhayes_tucson

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Posted 02 December 2013 - 01:02 AM

Where can we find the original Winroddier paper?

#23 drago

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Posted 02 December 2013 - 02:28 AM

hm. some years ago i try test four of my instruments - 90/1000 celestron achro, 66sd, 100ed, 15075 skywatcher, and 200 orion optics. i put hubble optics artificial star at about 80 metres away, and take a shots via canon eos 350d dslr in prime focus.
there vere a late autumn, as i remember, and my pics was processed with "DK" folk. intra and extrafocal taken defocus star to millimeters as an F number - F5 instrument is +5 and -5 milimeters from focal plane and so on.
i think, it is relatively easy method, and if in that distance ground current ruins anything, then it ruins also to look at more distant object, i thing.
if you interested, there is my test results:
http://www.astronomy...index.php/topic,38944.msg1072584.html#msg1072584

#24 bratislav

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Posted 02 December 2013 - 02:53 AM

> Where can we find the original Winroddier paper?

Wave-front reconstruction from defocused images and the testing of ground-based optical telescopes, Claude Roddier and Fran├žois Roddier

JOSA A, Vol. 10, Issue 11, pp. 2277-2287 (1993)

and the "original" original

C. Roddier and F. Roddier, "Combined approach to Hubble Space Telescope wave-front distortion analysis," Appl. Opt. 32, 2992-3008 (1993)

Bratislav

#25 Wade Van Arsdale

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Posted 02 December 2013 - 09:32 AM

The original WinRoddier research paper by Claude Roddier and Francois Roddier that can be downloaded from this link:
http://www.soft.bela...from_defocus...

In case above link is broken in this post:
http://tinyurl.com/pzk5b45

Sorry, I don't have a link to the Hubble research paper. If anyone does, would love to read that one as well.

Wade


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